This invention relates firstly to a device for injecting a treatment gas into a molten metal contained in a tank, and secondly a tank used in metallurgy and comprising at least one such injection device.
It is known how to treat a molten metal flow before casting it in the form of a metallurgical product, the molten metal possibly consisting particularly of aluminium, an aluminium alloy, magnesium or a magnesium alloy. The molten metal treatment is generally aimed at eliminating dissolved gases, particularly hydrogen, and also dissolved impurities such as alkaline metals, and solid or liquid inclusions that could reduce the quality of cast products.
Conventionally, this treatment step is done by injecting a treatment gas within the molten metal contained in a tank. The treatment gas may consist of an inert gas insoluble in the molten metal such as argon, or a reactive gas such as chlorine, or a mix of these gases.
The inert and insoluble gas absorbs the dissolved gas by a dilution effect and transports it with it. The reactive gas reacts with some dissolved impurities and thus generates liquid or solid inclusions that, like those already present in the molten metal, can be eliminated by a filtration operation.
U.S. Pat. No. 5,846,479 describes an in line treatment tank for a molten metal flow comprising several nozzles fixed in one wall of the tank. Part of each nozzle is located outside the tank and another part of the nozzle comprises an end hole housed inside the tank. However, this end hole has a very small diameter that can get blocked by the molten metal and metal oxides.
This hole can be cleaned after stopping the installation and opening the tank, from inside the tank. However, this is a laborious operation that causes loss of time and interrupts the treatment process.